Lesson Notes By Weeks and Term - Senior Secondary 2

Plant hormones

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TERM – 2ND TERM

WEEK ELEVEN

Class: Senior Secondary School 2

Age: 16 years

Duration: 40 minutes of 5 periods each

Date:

Subject: Biology

Topic: Plant Hormones

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

  1. Define plant Hormone
  2. Identify plant Hormones
  3. Identify 4 functions of plant Hormones
  4. Differentiate between sexual and asexual reproduction.

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

PRESENTATION

TEACHER’S ACTIVITY

STUDENT’S

ACTIVITY

STEP 1

INTRODUCTION

The teacher introduces plant Hormones and identify various plant Hormones.

Students pay

attention

STEP 2

EXPLANATION

Teacher discusses the functions of plant Hormones.

Students pay

attention and

participate

STEP 3

DEMONSTRATIO

N

Teacher discusses the effects of auxins  on plant processes.

Students pay

attention and

participate

STEP 4

NOTE TAKING

The teacher writes a summarized

note on the board

 

The students

copy the note in

their books

 

NOTE

PLANT HORMONES

Plant hormones, also known as phytohormones, are chemical messengers that regulate various physiological processes in plants. These hormones play a crucial role in plant growth, development, and response to environmental stimuli. Below are some key plant hormones:

  1. Auxins: stimulate cell elongation, control apical dominance, and participate in the formation of roots and fruits, e.g Indole-3-acetic acid (IAA).
  2. Gibberellins: This are hormones responsible for promoting stem elongation, germination, and flowering. For example, Gibberellic acid (GA).
  3. Cytokinins: Stimulate cell division, influence apical dominance, and delay senescence (aging) in leaves, e.g. Zeatin.
  4. Abscisic Acid (ABA): This hormone Inhibits growth, induces seed dormancy, and promotes stomatal closure during water stress.
  5. Ethylene: Regulates fruit ripening, senescence, and responses to stress (such as flooding or mechanical damage).
  6. Salicylic Acid: Involved in plant defense against pathogens and triggers systemic acquired resistance.

 Functions of Plant Hormones

  1. Cell Elongation and Division:Auxins and cytokinins stimulate cell elongation and division, respectively.
  2. Apical Dominance:Auxins control apical dominance, promoting the growth of the main shoot over lateral buds.
  3. Seed Germination:Gibberellins promote seed germination and seedling growth.
  4. Root Development:Auxins play a role in root development and branching.
  5. Stress Response:Abscisic acid and ethylene regulate responses to environmental stress, such as drought or flooding.
  6. Fruit Ripening:Ethylene is involved in the ripening of fruits.
  7. Defense Mechanisms:Jasmonates and salicylic acid play roles in plant defense against pathogens and herbivores.

Effects of Auxin on Plant Processes

  1. Lateral Development:

    - Stimulation of Growth: Auxins promote cell elongation, which can stimulate lateral (side) shoot development. This is particularly evident in the inhibition of apical dominance, allowing lateral buds to grow.

  1. Leaf Fall (Abscission):

   - Inhibition: Auxins typically inhibit leaf abscission. They help maintain leaves on the plant by preventing the formation of the abscission zone, a region where the leaf detaches.

  1. Initiation of Adventitious Roots:

   - Stimulation: Auxins play a crucial role in the initiation and development of adventitious roots. When applied to stem cuttings or wounded plant parts, auxins encourage the formation of roots, aiding in vegetative propagation.

Modern Applications of Plant Hormones:

  1. Auxins:

   - Rooting Agents: Used in horticulture for rooting cuttings to propagate plants.

   - Fruit Thinners: Applied to reduce fruit load, promoting larger and healthier fruits.

  1. Gibberellins (GAs):

   - Seedless Fruit Production: Applied to induce seedless fruit development (e.g., seedless grapes).

   - Malting in Brewing: Used to promote the growth of barley for malting in the brewing industry.

  1. Cytokinins:

   - Delaying Senescence: Used to extend the shelf life of certain fruits and vegetables.

   - Micropropagation: Applied in tissue culture for rapid multiplication of plants.

  1. Abscisic Acid (ABA):

   - Drought Tolerance: Used to enhance drought tolerance in crops.

   - Seed Dormancy: Applied to induce and maintain seed dormancy for synchronized germination.

  1. Ethylene:

   - Fruit Ripening: Used to ripen fruits artificially during transportation and storage.

   - Floral Senescence: Accelerates senescence in flowers to extend the vase life of cut flowers.

  1. Salicylic Acid:

   - Disease Resistance: Used to induce systemic acquired resistance against pathogens.

   - Post-Harvest Quality: Applied to maintain post-harvest quality in fruits and vegetables.

In Relation to Agricultural Practices:

  1. Early Flowering: Application of specific hormones, such as gibberellins, can be used to promote early flowering in certain crops, allowing for accelerated production cycles.
  2. Crop Harvest: Hormones like ethylene are used to regulate the timing of fruit ripening, ensuring that crops are harvested at optimal stages of maturity for better quality.
  3. Weed Control: Synthetic auxin herbicides, such as 2,4-D, mimic the action of natural auxins and are used for weed control. They disrupt normal plant growth processes in susceptible plants.

EVALUATION: 1. What are plant Hormones

  1. Identify 4 functions of plant Hormones
  2. Discuss the effects of auxins on plant processes.

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively